The present invention relates in general to a group control for elevators and, in particular, to a group control for immediately allocating destination calls.
Many known elevator group control systems include call registering devices arranged on the floors, by means of which calls for desired floors of destination can be entered. The entered calls are stored in floor and car call memories assigned to the elevators of the group where a call characterizing the entry floor is stored in the floor call memory and the calls characterizing the destination floors are stored in the car call register memory. Selectors assigned to each elevator of the group indicate the floor of a possible stop. First and second scanners are assigned to each elevator of the group. The first scanner operates during a cost of operation calculation cycle to store for each floor the costs in a cost memory. The second scanner operates during a cost comparison cycle of the costs for all elevators by means of which the entered call is assigned to the car of the elevator group which exhibits the lowest operating costs.
Such a group control is shown in the European patent application No. EP-A 0 246 395 where the assignments of the cars to the entered calls can be optimized in time. The car call memory of an elevator of this group control consists of a first memory containing assigned destination floor calls and additional memories assigned to the floors in which the desired floor calls entered at the respective floors, but not yet assigned to a car, are stored. A device, by means of which the entered calls are assigned to the cars of the elevator group, includes a computer in the form of a microprocessor and a comparator device. The computer calculates at each floor, during a scanning cycle of a first scanner, from at least the distance between the floor and the car position indicated by a selector, the intermediate stops to be expected within this distance and the load in the car, a sum proportional to the time losses of waiting passengers at the floors and in the car. In that case, the current car load is corrected by factors which correspond to the presumable numbers of boarding passengers and alighting passengers at future intermediate stops and which factors are derived from the numbers of boarding passengers and alighting passengers during past operations.
If the first scanners encounter a not yet assigned floor call, then the calls entered at this floor for desired floors of destination, stored in the further memories of the car call memory, are also taken into account. A sum proportional to the new floor calls is therefore determined and a total sum is formed. This total sum, also termed cost of operation, is stored in a cost memory by floor. During a scanning cycle of a second scanner, the operating costs of all elevators are compared with each other by means of the comparator device. An assignment command is stored in an assignment register of the elevator with the lowest operating cost, which command designates that floor to which the respective car is optimally assigned in time.
The scanning of all floors in the upward and downward directions and the calculation of the operating costs for each floor, whether a call is present or not, as well as the scanning of all floors for the purpose of the comparison of the operating costs at least at the floors with new calls, requires a relatively large amount of computing time and storage capacity as well as an expensively structured car call memory. On the other hand, an already assigned call, if it has not yet been transferred to the drive control of the elevator concerned, can be allocated to another elevator by reason of a later calculation and comparison cycle. Also, it is advantageous that operating costs are calculated for floors for which no calls have been entered, so that merely the additional operating costs need be calculated upon the registering of a call.
The operating costs formula, which forms the basis of the assignment procedure described in the above-identified patent specification, apart from the already mentioned factors for the calculation of the probable numbers of boarding and alighting passengers at a future stop, includes a factor of delay time (t.sub.v) at an intermediate stop and a factor of traveling time (m.multidot.t.sub.m) of an elevator, which factors are likewise only approximate average values. In this case, the traveling times of the individual elevators can differ from one another for the same number of floors to be traveled due to unequal operating drives, inaccuracies in the floor distances or, in the case of high performance elevators with a leading selector, the different speeds generated. Thus, the assignment procedure can lead to inaccurate results. The operating costs are moreover ascertained merely over a limited range of the travel path, which is however completely sufficient for the comparison of the elevators one among the other, but supplies no indications of the actual waiting times of all passengers participating in the elevator system traffic at the instant of calculation.
In the European patent No. EP-PS 0 301 173, it was proposed to replace the probable numbers of boarding and alighting passengers by the number actually to be expected as an improvement in the operating costs formula. In this case, a sum is formed from the number of the calls entered at a floor and the number of the calls designating this floor as a travel destination and this sum is stored as load value in a load memory, wherein the load value is taken into account in the computation of the operating costs of the floor concerned. If the load values are not changed in the time between the entry of a new call and the transfer of this call to the drive control of the elevator concerned, then the call assignment can be regarded as optimal.
There is shown in the European patent application No. EP-PA 88 110 006.9 a group control of the above-described type which leaves a call first assigned to a car with that car. Thereby, the identity of the assigned car can be signaled to the waiting passengers on the floors almost immediately after the call is entered. Since it can be assumed as improbable that the load values have changed in the very short time between the call entry and assignment, the assignment is optimal at the instant of assignment, at least with respect to the future car load. However, since the initially and definitively assigned call no longer participates in the optimizing process and further calls could be entered until the transfer of this call to the drive control concerned thereby changing the load values accordingly, the assignment can no longer be regarded as optimal in such a case.